1. Field of the Invention
This invention relates to an electromagnetic actuator system, and more particularly relates to an electromagnetic actuator system using a stepper motor operated in a position-sensed double closed loop mode, via an electronic commutator, by dynamic position and anomaly corrected control provided by a computer as a single amplitude-variable input signal.
2. Description of the Prior Art
To generate torque an ordinary D.C. motor has many windings which are automatically switched on or commutated at the appropriate time by brushes, or in a brushless D.C. motor by a position sensor and electronic switches.
Stepping motors have a high force or torque output. Since they can produce this torque at very low speeds they are quite attractive as direct drive actuators for robots. Unfortunately, the common "control" schemes for stepping motors use sequencing logic which can only position the motors at their cardinal step positions. This conventional control does not operate well at high speeds or with varying loads. For a direct drive application it is desirable that the stepping motor position itself between cardinal steps. The usual approach of "micro-stepping", providing equilibrium point between cardinal step positions through a balancing choice of coil currents, is cumbersome, doesn't account for motor dynamics, and is wasteful of power. Secondly, control of delivered torque or force is a desirable trait in a robot actuator, but such control is difficult with conventional stepper motor control laws. Motor control laws known for DC servomotors have heretofore not been conveniently applied to stepper motors.
The following are representative of the prior art: